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. 2022 Oct 22;13:6295. doi: 10.1038/s41467-022-34128-5

Fig. 1. Construction of transgenic silkworms.

Fig. 1

a Schematic diagram of SGs producing cocoon silk. The silk fibrils are long chains formed by Fib-H/Fib-L/P25 polymer fibroin units synthesized by the PSG. The silk fibroin heavy chain protein (Fib-H), silk fibroin light chain protein (Fib-L), and P25 protein synthesized by PSG cells are secreted into the lumen as fibroin units and then are transferred to the MSG as a metastable high-concentration aqueous colloid. In the MSG lumen, the aqueous colloid of silk fibroin is surrounded by sericin C (sericin 1 is the main composition), which is secreted by the back end and middle part of the MSG, and then is surrounded by sericin B (mixed sericin) and sericin A (sericin 3 is the main composition), which are secreted by the middle and anterior part of the MSG. b Technical strategy. Efficient transgenic expression of SER3 recombinant protein in silkworm PSG cells, to achieve secretion into the PSG lumen and to incorporate water-soluble sericin 3 recombinant protein into the silk fibroin colloidal solution, alter the metastable state of silk fibroin protein polymers and further affect the silk fiber structure after self-assembly. SM, sericin microsomes expressed in the PSGs and incorporated into the cocoon silk fibrils. Vac, vacuoles in SM. SER, transgenic mutant system for expression of the sericin 3 recombinant gene in the PSG. WT, wild type. c Transgenic piggyBac vector. To enhance the expression and secretion of sericin 3protein (SER3) by PSG cells, the Fib-H gene promoter sequence and 1416 bp of its base sequence containing the signal peptide were introduced upstream of the sericin 3 gene (Ser3) sequence with a length of 3120 bp (Supplementary Sequence 1). The EGFP reporter gene sequence and the 333 bp base sequence at the 3’ end of the Fib-H gene were connected downstream of the Ser3 gene sequence. Moreover, an artificial promoter, 3 × P3, composed of three tandem PAX-6 transcription factor binding sequences, was specifically expressed in the silkworm eyes and nervous system, and was used to regulate the RFP reporter gene.